Replacement of prosthetic joints often becomes necessary, even in the best of situations. Sometimes an infection develops or a prosthetic fails, but other times, the prosthetic is simply worn out. Regardless of the reason, replacement (or “revision” as it is sometimes called) poses a difficult problem for a surgeon in that more bone will need to be removed to enable the new prosthetic to fit tightly, but it is best to remove as little additional bone as possible.
In hip arthroplasty, for example, a prosthesis stem portion is placed in the intramedullary canal of the femur and stabilized with a cement mantle. When a revision joint arthroplasty surgery is performed, the stem from the previous prosthesis needs to be removed and consequently so does the cement mantle used for the implant. To remove the cement mantle a surgical drill or bur is used. All previous techniques that use drills and burs to remove the cement mantle, however, also run a high risk of removing additional bone unnecessarily.
To combat this problem, some previous technologies focused on guiding the drill so that it is aligned to not do any damage. U.S. Pat. No. 5,047,035 to Mikhail et al. discloses a system for performing hip prosthesis revision surgery that includes a trial femoral component having a passageway which, upon insertion into the cavity remaining after removal of the original prosthesis, provides guide means for drilling a channel to receive a guide wire which, upon removal of the trial femoral component, serves as guide means for progressively larger reamers. Alternatively, stopping a surgical drill once it breaks through a workpiece so that no unintended damage is done is disclosed in U.S. Pat. No. 8,463,421 to Brett et al. In Brett, a control breakthrough method is described wherein the speed of the drill bit is controlled by continually measuring the force and torque on the drill bit during the procedure and calculating the rate of change in the force and torque so that soft tissues are not damaged. Neither of these technologies, however, has been brought to bear on the problem of removing cement while maintaining bone during revision surgery.